The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device which enables a high-quality display by overcoming a display defect attributed to the displacement of a light shielding film at a multiple exposed portion generated when the light shielding film is formed by divided exposure two or more times with 1:1 exposure using an exposure mask smaller than a size of a display region.
As a high-definition color monitor for a computer or other equipment, a liquid crystal display device has been popularly used. The liquid crystal display device is basically configured such that a so-called liquid crystal panel is formed by sandwiching a liquid crystal layer between two (a pair of) substrates at least one of which is formed of a transparent glass or the like. The liquid crystal display device is classified by a driving circuit into a type in which given pixels are turned on and off by selectively applying a voltage to various electrodes for forming pixels which are formed on the substrate of the liquid crystal panel and a type in which the above-mentioned various electrodes and the active elements for pixel selection are formed and given pixels are turned on and off by selecting the active elements.
Particularly, the latter-type liquid crystal display device is referred to as an active-matrix type and forms a main stream of the liquid crystal display device in view of excellent features such as the excellent contrast performance, the rapid display performance and the like. As the active-matrix type liquid crystal display device, there have been known a so-called vertical electric field system in which an electric field which changes the orientation direction of the liquid crystal layer is applied between electrodes formed on one substrate and electrodes formed on another substrate, a so-called lateral electric field system (also referred to as an IPS system) in which the direction that an electric field is applied to the liquid crystal layer is arranged substantially parallel to a substrate surface and the like.
The liquid crystal panel which constitutes the above-mentioned various liquid crystal display device is provided with a pixel circuit formed of active elements, pixel electrodes and the like on a main surface of one of a pair of substrates, color filters of plurality of colors which are defined by a light shielding film (also referred to as a black matrix hereinafter) are provided to a main surface of one substrate or another substrate, and both main surfaces of both substrates are arranged to face each other in an opposed manner and are laminated to each other and the liquid crystal layer is sandwiched in a laminated gap.
In the manufacture the liquid crystal panel for a large-sized liquid crystal display device having a nominal size of 30 inches or more, the reduction of manufacturing cost is limited with respect to an exposure mask having the substantially equal size as a display region of the liquid crystal panel and hence, in many cases, various lines, pixel circuits, or a black matrix and color filters which are formed on the respective substrates are formed by a 1:1 exposure method (proximity exposure) performing the divided exposure of two or more times using an exposure mask smaller than the display region of the liquid crystal panel.
FIG. 11 is an explanatory view for explaining steps of forming a light shielding film by the 1:1 exposure method. Hereinafter, the explanation is made with respect to the IPS type liquid crystal panel as an example in which the black matrix is formed on another substrate (also referred to as a color filter substrate or a CF substrate) of a pair of substrates which constitute a liquid crystal panel. However, the same goes for the TN type liquid crystal panel in which the black matrix and the color filters are formed on one substrate (also referred to as a TFT substrate since thin film transistors are generally used as active elements). When the black matrix is formed on the CF substrate SUB2 by performing the divided exposure twice by the 1:1 exposure method, first of all, as shown in FIG. 11(A), an exposure mask MSK having a X-direction size of an effective exposure region shorter than a lateral-direction (X) size of the CF substrate SUB2 on which a photosensitive black matrix material is applied is used. In the drawing, the effective exposure region which constitutes the display region is indicated by a drawing pattern BP of the black matrix. Here, the black matrix which defines the respective color pixels in an X-direction is omitted from the drawing.
In FIG. 11(B), the CF substrate SUB2 is mounted on a stage (not shown in the drawing) of an exposure machine, the exposure mask MSK is placed on one half of the CF substrate SUB2, another half and an outer peripheral portion which constitutes a picture frame in a product are covered with a shutter ST1 and, thereafter, the first exposure is performed. Here, the shutter ST1 is arranged to cover also a portion of the drawing pattern BP of a boundary portion of the region to be exposed.
Next, the stage is moved to position the exposure mask MSK on another half side of the CF substrate SUB2, wherein one half and the outer peripheral portion which constitutes the picture frame in the product which are exposed by the first exposure are covered with a shutter ST2 and the second exposure is performed. Also in this case, the shutter ST2 is arranged to cover by forming a multiply-exposed portion of several mm, for example, in a direction such that the a portion of the drawing pattern BP at a boundary portion of a post-exposed region is connected (FIG. 11(C)).
As shown in FIG. 11(D), the drawing pattern is exposed in a given region AR of the CF substrate SUB2. The drawing pattern is developed and is baked to obtain the black matrix BM. The obtained black matrix BM generates an error δa which is displaced in the vertical direction (Y) in the drawing at a position of a multiply-exposed portion DE having a width of several μm (for example, ±5 μm) depending on the accuracy of the movement of the stage of the exposure machine (FIG. 11(E)). Here, R, G, B in FIG. 11(E) respectively indicate pixel regions on which red, green and blue color filters are formed (sub pixels, a color pixel being constituted of three sub color pixels of R, G, B in a color display).
Here, as a literature which discloses the liquid crystal display device of this type, Y. M. Tak, et al “SID 02 DIGWST” pp. 1281–1283 “48.2 Panel Design & Simulation of 40-in. TFT-LCD (literature 1) can be named.